1. Field of the Invention
The present invention relates in general to transducers, and more particularly to mass loaded acoustic dipole transducers capable of radiating and receiving acoustic energy at very low frequencies and also capable of withstanding high ambient pressures.
2. Background Discussion
Underwater sound dipole transducers can be designed to withstand high pressures by the use of a structurally enclosed housing which is operated so as to be set into translational motion by an enclosed attached transducer. These devices have been called “shaker box transducers”. In operation the housing (“box”) is moved back and forth in the medium alternately creating a pressure increase on one side and pressure decrease on the opposite side which results in a dipole beam pattern from the housing acting as a dual-sided piston radiator. The attached interior driving transduction device can be constructed from piezoelectric ceramic such as PZT. One such structural form of the PZT is referred to as the bender type which allows a large displacement at low frequencies. In this case the ends of the bender are attached to the housing and the center part of the bender moves laterally against the attachment causing the box to move. In previous designs the inertial reaction mass has been based only on the inherent dynamic mass of the bender structure itself.
One form of transducer is shown in my earlier U.S. Pat. No. 4,754,441 entitled “Directional Flextensional Transducer” issued on Jun. 28, 1988. This prior art patent illustrates an elliptical transducer that is driven into a dipole mode by a bending action and including an outer shell that supports a drive stack that may be comprised of piezoelectric or magnetostrictive material. However, in this transducer the stack does not use any central reaction mass.
It is an object of the present invention to provide an improved electro-mechanical transduction apparatus constructed and arranged so as to increase the motion of the housing and create greater acoustic intensity by attachment of a reactive inertial mass or masses to the center of the bender reducing the motion at that point and translating this motion to the edge mount on the box causing greater box or housing motion.
Another object of the present invention is to provide an improved acoustic transducer in which the resonance frequency and mechanical Q are lowered through the attachment of the aforementioned mass or masses.